Re: [RFC][PATCH] mm: couple rcu and memory reclaim

From: Balbir Singh
Date: Mon Sep 24 2007 - 08:49:21 EST

Peter Zijlstra wrote:
>>> Only kswapd can do this, direct reclaim has deadlock potential.
>> Yes, but not in all cases, do you want to add any gfp_mask
>> based smartness for direct reclaim?
> gfp_mask doesn't carry the needed information. It depends on whether
> the current context holds a rcu_read_lock().

What I meant was that nobody would hold rcu_read_lock() and pass
gfp_mask of GFP_KERNEL in scan_control or to do_try_to_free_pages()

> so something like:
> rcu_read_lock()
> foo = kmalloc(sizeof(foo))

At this point, you really can't use GFP_KERNEL, since rcu_read_lock()
disables pre-emption in the current kernel, ideally you should see
a might_sleep() BUG.

> new_slab()
> __alloc_pages()
> try_to_free_pages()
> synchronise_rcu() <-- deadlock
> rcu_read_unlock()

Warm Regards,
Balbir Singh
Linux Technology Center
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